Tunable electron discharge devices and cavities



p 19, 1967 v w. J. HQNEYBALL 3,343,106

TUNABLE ELECTRON DISCHARGE DEVICES AND CAVITIES Filed March 19, 1965 United States Patent 3,343,106 TUNABLE ELECTRON DISCHARGE DEVICES AND CAVITIES Walter John Honeyball, Chelmsford, England, assignor to English Electric Valve Company Limited, London, England, a British company Filed Mar. 19, 1965, Ser. No. 441,266

Claims priority, application Great Britain, Apr. 1, 1964,

13,441/ 64 6 Claims. (Cl. 333-83) The invention relates to tunable electron discharge devices and cavities. Tuning of a cavity in a tunable microwave device such as a tunable magnetron is usually accomplished in present day practice by a plunger which is adjustable in position within the cavity. However, the control of the position of such a plunger presents considerable practical difiiculties because the interior of such cavities are usually evacuated to operate at pressures far below atmospheric and accordingly, if an extremely operable mechanical control is used to adjust the plunger, the mechanical linkage must pass through the wall of the cavity in a vacuum tight manner. This obviously imposes considerable practical difficulties. Common practice is to provide a flexible diaphragm or bellows which in elfect forms part of the vacuum tight wall of the cavity and use this to transfer mechanical adjustment motion from the outside to the inside of the cavity but known arrangements of this kind have the defect that the diaphragm or bellows is subjected to external atmospheric pressure which tends to collapse it and provides a bias force trying to push the plunger further into the cavity. This involves that the control force required to push the tuning plunger into the cavity is considerably less than that required to pull it out and the external mechanical tuning mechanism is therefore undesirably stressed. The present invention seeks to overcome these defects.

According to this invention, in an evacuated tunable cavity tun-able by at least one plunger which is movable therein said plunger is carried on a support member which passes through and is slidable within a hole in the cavity wall and is carried by a further member on both sides of which are extensible bellows connecting the same to two fixed parts, said bellows being extensible substantially only in a direction parallel to the direction of sliding movement of the support member and the whole arrangement being such that the bellows, further member, fixed parts and cavity wall enclose an evacuated space which is in communication only with the evacuated interior of the cavity.

The invention is illustrated in the accompanying drawings in which:

FIGURE 1 is a schematic section of one embodiment of the invention, and

FIGURE 2 is a similar view of a modification. Like references denote like parts in both figures.

Referring to FIG. 1, the wall 1 is part of the Wall of a magnetron having an evacuated interior 2 and a resonant cavity 3 the resonant frequency of which is adjusted by adjusting the positions of plungers 4 which are movable in a direction parallel to the axis 5 of the cavity by rods 6 to which they are attached. The rods 6 pass through holes 7 in the wall 1 and are attached at their far ends to an annular plate 8. Means (not shown) are provided for adjusting the position of the plate '8 in a direction parallel to the axis 5 of the cavity so as to tune the cavity. One side of the plate 8 is connected to the wall 1 by a vacuum tight flexible cylindrical bellows 9 and the other side of the said plate is similarly connected by a further similar bellows 10 of the same diameter as bellows 9 to a fixed annular plate 11 sealed to the wall of the magnetron. The two bellows 9 and 10 with the plate 8 Patented Sept. 19, 1967 between them, the plate 11 and the wall 1 enclose a space 12 which is in communication with the interior space 2 via the inevitable leakage between the rods 6 and the walls of the holes 7 and this space 12 is evacuated so that, in operation, it is under the same vacuum as the space 2. The utilization of the bellows 9 and 10 of substantially the same diameter results in each of these bellows defining substantially the same effective area by their intersection with the plate 8 on each side thereof. That is, the area on each side of the plate 8 which is subjected to the vacuum is substantially equal to the area on the opposite side of such plate. Slight variations in the equality of this area may, of course, be eifected in order to overcome extraneous biasing forces upon the plate 8 such as, for example, the weight of the plate 8 and the members attached thereto. There is thus no force due to atmospheric pressure tendency to move the plate in one direction or the other and the vacuum is not affected by tuning. The mechanical means (not shown) for moving the plate 8 is of course, attached thereto outside the bellows structure 910.

FIGURE 2 ShOWs an embodiment in which hydraulic pressure adjustment is used to vary the position of the plate 8 for tuning purposes.

Referring to FIG. 2 a plate 13 formed as a flange-like extension to the wall of the magnetron is provided and the plates 8 and 11 are also extended outwardly. A further pair of cylindrical bellows 14 and 15 concentric with bellows 9 and 10 connect the two sides of the plate 8 to the plates 11 and 13 as shown. Plate 8 is of solid material and divides the space bounded by the four bellows 9, 10, 14, 15 and by the plates 11 and 13 into two spaces 18 and 19.

Ports in the plates 11 and 13 are connected by hydraulic pressure pipes 16 and 17 (gas or liquid pressure may be used and the term hydraulic is herein employed to cover both) to hydraulic control equipment whereby the pressures in the spaces 18 and 19 may be differentially varied to adjust the position of the plate 8 and therefore of the plungers.

I claim:

1. Apparatus comprising an evacuated tunable cavity tunable by at least one plunger which is movable therein wherein the said plunger is carried on a support member which passes through and is slidable within a hole in the cavity wall and is carried by a further member on both sides of which are extensible bellows defining substantially equal effective areas and connecting said further member to two fixed parts, said bellows being extensible substantially only in a direction parallel to the direction of sliding movement of the support member and the whole arrangement being such that the bellows, further member, fixed parts and cavity wall enclose an evacuated space which is in communication only with the evacuated interior of the cavity.

2. Apparatus as claimed in claim 1 wherein the bellows are similar, cylindrical and co-axial.

3. Apparatus as claimed in claim 1 wherein there is a plurality of plungers each carried by a support member comprising a rod which is slidable endwise in a hole in the cavity wall, the rods being carried by said further member, said further member comprising an annular plate and the two bellows connecting opposite faces of said plate to said two fixed parts, said two fixed parts comprising further plates, one on either side of the annular plate and parallel thereto.

4. Apparatus as claimed in claim 1 wherein mechanical adjustment means, attached to the further member outside the bellows, are provided for mechanically moving said further member in the direction of sliding movement of the support member or members.

5. Appaartus comprising an evacuated tunable cavity having plunger means movable therein for tuning of said cavity, movable support means connected to said plunger means, extensible bellows means for sealing said evacuated cavity and maintaining said movable support means in an unbiased condition, said bellows means connecting said support means to two fixed parts, said bellows means, support means and two fixed parts defining an evacuated space in communication with said evacuated cavity.

6. Apparatus comprising an evacuated tunable cavity tunable by at least one plunger which is movable therein wherein the said plunger is carried on asupport member which passes through and is slidable within a hole in the cavity wall and is carried by a further member on both sides of which are extensible bellows connecting said further member to two fixed parts, said further memberprojecting outwardly of said bellows, said bellows being extensible substantially only in a direction parallel to the direction of sliding movement of the support member and the whole arrangement being such that the bellows, further member, fixed parts and cavity wall enclose an evacuated space which is in communication only with the evacuated interior of the cavity, a further pair of bellows, attached one each side of the outwardly projecting portion of said further member further connecting said further member to said two fixed parts so that there is an enclosed volume divided into two spaces by said outwardly projecting portion between the two pairs of bellows, hydraulic adjusting means, operative to adjust the difference of the hydraulic pressures in said two spaces, being provided for moving said further-member in the direction of sliding movement of the, support member.

References Cited t UNITED STATES PATENTS 2,500,430 3/1 950 Pierce 33383 2,932,203 4/1960 Peters 74l8.2

FOREIGN PATENTS 370,117 2/ 1923 Germany.

HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

L. ALLAHUT, Assistant'Examirier.

Disclaimer 3,343,106.Walte J 07m H o'neyball, Chelmsfm'd, England. TUNA BLE ELEC- TRON DISCHARGE DEVICES AND CAVITIES. Patent dated Sept. 19, 1967. Disclaimer filed July 24, 1970, by the assi nee, English Eleetrz'c V (LZU Company Limited. Hereby disclaims claims 1, 2, 4; and 5 of said patent.

[Oflicial Gazette November 10, 1.970.] 

5. APPARATUS COMPRISING AN EVACUATED TUNABLE CAVITY HAVING PLUNGER MEANS MOVABLE THEREIN FOR TUNING OF SAID CAVITY, MOVABLE SUPPORT MEANS CONNECTED TO SAID PLUNGER MEANS, EXTENSIBLE BELLOWS MEANS FOR SEALING SAID EVACUATED CAVITY AND MAINTAINING SAID MOVABLE SUPPORT MEANS IN AN UNBIASED CONDITION, SAID BELLOWS MEANS CONNECTING SAID SUPPORT MEANS TO TWO FIXED PARTS, SAID BELLOWS MEANS, SUPPORT MEANS AND TWO FIXED PARTS DEFINING AN EVACUATED SPACE IN COMMUNICATION WITH SAID EVCACUATED CAVITY. 